1. Field of the Invention
The present invention relates to a printer which allows unit printing of a plurality of pages, particularly to a printer which can reduce printing hours on the whole, and a control program product thereof.
2. Description of the Related Art
Use of page printers which can print by unit of a page has been rapidly spreading in offices and private residences in recent years, and an acceleration of printing speed, price reduction, and improvement in quality are desired. Of these so far, various techniques have been developed for accelerating printing speed. One of these techniques is unit printing of a plurality of pages.
This technique is for executing printing of a plurality of pages at one time in one printing processing. When two pages are printed at one time in one printing processing, it is called “2 page unit printing” or “2 up printing”, and when n pages are printed at one time in one printing processing, it is called “n page unit printing” or “n up printing”.
This unit printing of a plurality of pages is explained in detail hereinafter, giving an example of 2 up printing. For example, a page printer, which can print a paper of size A3, usually has a transfer body (intermediate transfer medium) for transferring a toner image to a paper; this transfer body has a 1 page size of paper of size A3. Therefore, only one page of size A3 can be printed in one printing processing. Here, if it is color printing, one time of printing processing is concretely performed such that 4 colors of toner are adhered to the transfer body one by one in order, by 1 rotation of the transfer body for 1 color, and while the last color of toner is being adhered, the toner image of 4 colors that were adhered is transferred from the transfer body to a paper. Accordingly, one time of printing processing requires more than 4 rotations of the transfer body.
With this type of page printer, by regarding printing images of a portion of 2 pages of size A4 the same as a printing image of 1 page of size A3, processing of 2 pages of size A4 can be performed in the same processing time as the printing processing for 1 page of size A3. Thus, printing 2 pages by 1 printing processing is called 2 up printing.
With this printer for size A3 which can perform 2 up printing, when printing an image of only 1 page of size A4 (1 up printing or 1 page printing), an area of the transfer body to which a toner is adhered becomes half. However, in color printing, adhesion of 4 colors of toner to the transfer body is performed, as described before, by one rotation of the transfer body for each color, regardless of where the colors adhere. Therefore, 4 rotations of the transfer body are required for printing 1 sheet of paper of size A4. The rotation speed of the transfer body is usually fixed, therefore, the time required for printing 1 sheet of paper of size A4 is almost the same as the time required for printing 1 sheet of paper of size A3, that is, the time required for printing images of 2 pages of size A4 by 2 up printing. Accordingly, when printing 2 pages of size A4, if 2 up printing is possible, it can greatly reduce the printing time, compared to printing each paper (1 up printing).
However, in order to perform 2 up printing, data for 2 pages has to be output from the controller of the printer to the engine member which performs actual printing. In Short, the controller has to perform data processing for the 2 pages and supply the data to the engine member, and the engine member has to be ready for printing, otherwise, 2 up printing can not be performed.
Therefore, if it takes time for data of page 2 to reach the engine member after data for page 1 has reached the engine member, there may be cases where printing can be finished earlier by performing 1 up printing for each page than by waiting for the data (to reach the engine member) and performing 2 up printing. Therefore, whether the 2 up printing is effective depends on the waiting time for the data of the 2 pages to reach the engine. And the critical waiting time in which the effect of the 2 up printing can be achieved, is called a maximum waiting time T. This waiting time is obtained by deducting the time required for 2 up printing from the time required for printing 2 pages by 2 times of 1 up printing. If the data of the 2 pages reaches the engine member by the maximum waiting time T, 2 up printing is effective.
For example, if the time required for printing 2 pages by 2 times of 1 up printing is 20 seconds and the time required for 2 up printing is 11 seconds, the maximum waiting time T is 9 seconds. If the data of page 2 reaches the engine member within 9 seconds after the data for page 1 reaches the engine member, it means that 2 up printing is effective.
The unit printing of a plurality of pages has been explained so far using the example of 2 up printing. n up printing of more than 3 pages is similar. There is a time limit, which is based on a difference between the time required for printing m pages in m page unit printing as well as printing 1 page in 1 page unit printing for page m+1, and the time required for printing m+1 pages in m+1 page unit printing. Accordingly, if the data for page m+1 does not reach the engine member during the maximum waiting time, there is no benefit to wait for page m+1 (to reach the engine member) and perform m+1 up printing.
Thus, the time required for data of the next page to reach the engine member is the key to efficiently control n up printing, but this waiting time changes depending on the amount of the data of the page and the condition of communication between a host computer for giving printing orders and a printer. Therefore, the waiting time can not be easily predicted.
As one of the methods of controlling n up printing, a method exists of waiting for data of next page (to reach the engine member) until a certain time (for example, a maximum waiting time T) and performing printing up to the present page if the data does not reach the engine member by the certain time. But, in this method, printing is always started after waiting for the data until the certain time. Therefore, if there are many cases where the data of the next page does not reach the engine member by the certain time, there is only a small amount of time saved in spite of the total waiting time. And so, this method is not necessarily an effective control method.
Therefore, the object of the present invention is to provide a printer which can shorten the time required for printing in unit printing of a plurality of pages, and a program product for controlling such printer.